Following is the USDA official report of WNV activity in the U.S. in 2001.

Equine Cases of West Nile Virus Infection in 2001: January 1 through December 31, 2001.There were 738 cases of clinical West Nile virus (WNV) infection reported in horses from 130 counties in 20 states (see the summary by state and county below). Of the 738 reported, 651 cases were verified through diagnostic testing at the National Veterinary Services Laboratories of USDA-APHIS. Of those, 640 were classified as confirmed cases and 11 as probable cases.